Antihalation and filter layers for photographic film



May 7, 1940 D. E. R. AYREs z-:r A1. 2.199,978 I ANTIHALATION AND FILTER LAYERS FOR PHOTOGRAPHIC FILM Filed nec. 1, 1958 v F//zer /ayef of h yafro/yzed /ac res/f7 conta/mn a /4 dye j l Emu/lons vercoa/'ng /ayer 0f hydrolyzed /ac ras/'f2 Derek EPA rs A/an ,Ba /ey Edwara. Knozz mw BY Q,

ATTORNEYS ANTIHALATIO AND FmrEn LAYERS Patented May 7, 1940 l FOR PHQTOGRAPHIO FILM Derek E. R. Ayres, Alan Batley, and Edward B.

Knott, Wealdstone, England, assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey sppueaann member 1, 193s, serial No. 243,386

In Great Britain December 9, 1937 '7 Claims.

` This invention relates to sensitive photographic elements having a. non-sensitized layer, such as an ant-ihalation layer, filter layer or protective layer.

I Layers such as these which have a function during the exposure of the light-'sensitive ele- I ment, often require to be readily removed by the processing baths to which the element is'sub- '.jected. Alternatively, if the layer itself is not l. removed it is essential that it be easily penetrated by the processing solutions so that, for

example any dye which it may contain can be decolorized. It is a great advantage to employ a layer which in plain water lswater resistant or u' insoluble, Vsince the employment of such a layer involves a minimum of risk of staining any objects, such as the operators fingers or an emulsion layer which may touch it. By "water resistant we mean that the layer remains undis- N solved and reasonably hard` in plain cold water and insoluble for times upwards of half an hour. Furthermore a sensitive material having such a layer can be made by first coating the support, e. g. glass, with that layer on the back and then 8l coating the front surface with sensitive emulsion bythe usual method which involves bringing the back of the support into. contact with a wet chilling surface. On this account, therefore, water soluble or water swellable preparations are 30 unsuitable. l

The present invention is based on the discovery that all of the .aforesaid advantages can be obtained by employing for a layer of the type described, the product obtained by partially 36 hydrolizing certain suitable fractions or constituents of natural resins, to an extent which is insufficient to render them Water soluble, but sufcient to render them softened in weak alkali, e. g. sodium carbonate, and preferably soluble n therein. A

In the accompanying drawing,

Fig. l is a sectionalview of a photographic film having thereon an antihalation layer made according to our invention, v

' 45 Fig. 2 is a sectional view of a multi-layer photographic film having a filter layer thereon according to our invention, and

Fig. 3 is a sectional view of a photographic film having thereon an overcoating layer made ac- 50 cording to our invention.

(a) Any natural lac can be divided into two portions e. g. by treatment with alkali solution into a fraction soluble therein and a fraction insoluble therein. The proportion of these frac- 55 tions depends upon the concentration of the a1- (cl. sis- 9) kali used. Whatever amount of alkali is used the 4 alkali soluble portion is termed for convenience the soft lac and the remaining portion is termed the hard. lac. Another way of separating soft and hard portions is by solvents e. g. toluene.

(b) In the caseof the hard lacs they are all suitable for the purposes of this invention provided that the proportion is not more than 90% of the whole lac by weight and that if the proportion of such lac is less than about 70% of the whole it is treated with HC1 in the subsequent hydrolysis. y

(c) In the case of the soft lacs they can be' used for the purpose of this invention, if the proportion of such lac is not morel than about 40% by weight of the whole lac. It may be necessary to polymerize it prior to the subsequent hydrolysis especially if thev proportion is less than about 10%. Y A part of any of the above possible fractions may be used. r

Preferably, we employ either a soft lac resin or a hard lac resin, and carry out the hydrolysis thereof by subjecting the lac to a caustic alkali, such as caustic soda in dilute methylated spiritior a time depending on the nature of the lac and the temperature employed. Whichever form of lac i's used it should previously have been freed from wax (which would otherwise remain insoluble in developer) and should be'bleached (as otherwise developer solution becomes objectionably coloured). When test samples show that the lac has reached the degree oi hydrolysis at which it is' softened in an alkaline solution, e. g. of sodium carbonate and preferably soluble therein but water resistant, the bulk is precipitated with dilute acid, preferably in the cold, washed free from acid and thoroughly dried. To make an antihalation layer with the product it is dissolved ina non-aqueous solvent such as methanol and in the solution is dissolved or dispersed a water soluble or water insoluble dye or a pigment. If the layer is one which is'merely softened in an alkaline developer but not removed entirely in such developer, then the dye or pigment may be one which is not decolorized in the processing baths, since such layers can usually be easily removed by rubbing with a swab of cotton wool, but if the layer is entirely removed during processing, it isvdesirable, although it is not essential that the dye or pigment be one which is decolorized in the baths. The degree of hydrolysis which is required has been found to be dependent to some extent upon the nature of the dye and this must, therefore, be taken into account when preparing the hydrolyzed lac. Thus We have found that usually the alkali soluble partially hydrolyzed lac made according to the present invention tends to become rendered rather less soluble in weak alkali by the presence therein of certain dyes e. g. Acid Fuchsine and in, such cases it is advisable to keep the concentration of dye down to a minimum. Since this invention only relates to the use 0f naturalresins, it is evident that the source of supply of the raw material will have some bearing on the precise procedure to be adopted in making the partially hydrolyzed product, for example, the time-of hy'- drolysis may need to be varied accordingly. Similarly, if one starts' with a sample of hard lac it usually requires somewhat diierent hydrolysis than the fraction known as soft lac, from the same raw shellac. If desired other substances e. g. those of a resinous or colloidal naturel e. g cellulose esters, may be incorporated in the layers oi' the present invention.

Our invention will be further describedby reerence to the following examples, which are, however, illustrative only:

EXAMPLES In all three examples below the starting product is a de-waxed whole lac with low resin content, having an acidvalue of say, 73 and a softening point of say 69 C. (softening-melting range, say 69-77 C.). For detail of the separation of lac fractions see Bhattacharya and Heath, London Shellac Research Bureau Technical Paper No. 16.

EXAMPLE 1 (a) Preparation of an 80 per cent bleached hard lac resin (that is, representing approximately 80 percent of the original whole lac) grams de-waxed whole lac (ground to 120 mesh) are stirred at 25 C. for 2 hours with a solution of 0.55 gram sodium carbonate in 'l5 ccs. water. The undissolved lac (approximately 80 per cent of the whole lac) is allowed to settle and the supernatant liquor drawn oil. The resin is then well-washed by decantation, filtered, collected and dried in air. Careful controlled bleaching is carried out by the recognized procedure,

by dissolving grams of the fractionated lac 'in 100 ccs. of a 3% sodium carbonate solution and gradually adding aqueous sodium hypochlorite solution untilthe lac solution becomes colorless. The lac is then precipitated with dilute sulphuric acid. It is well-washed, filtered, collected and dried Ain air to a moisture content of about 2 per cent. At this stage the fractionated bleached, hard lac should have an acid value about 66 and a softening 4point of about 80 C. (softeningmelting range 80-87 C.). The precise values depend of course upon the corresponding valu of the original lac.

(b) Hydrolysis 20 grams of the hard lac resin thus prepared are dissolved in ccs. spirit by warming. 'I'he solution is cooled and the lac hydrolysed by the addition of 160 ccs. 0.5N caustic soda solution.

y The solution is well agitated and the temperature (a) Preparation of should be changed to about 90 minutes.

.hydrolysed lac which has an acid value of about aieaevs to allow sedimentation and the liquor syphoned off. Fresh ice water is added, stirred and syphoned o again. .This procedure is repeated until the wash lwaters are neutral. 'I'he lac is then ltered in a centrifuge through linen. The lac which has an acid value of about 160 is then dried thoroughly by spreading out on open trays for several days.

v(c) Preparation of the backing mixture 10 grams hydrolysed lac are dissolved in 15 ccs. methanol in which has already been dissolved 0.5 g. Ink Blue dye. A layer of this solution is then applied to the glass plate etc. at the rate of say, 1/2 cc. per square foot.

EXAMPLE 2 11 per cent bleached soft Zac resin 25 grams de-waxed Whole lac (ground to 120 mesh) are stirred at 25 C. for 2 hours with a solution of 0.3 g. sodium carbonate in 75 ccs. water. The supernatant liquor is decantedoi,

the undissolved lac washed with water, the washings decanted oi and together-with the liquor are acidiiied with dilute sulphuric acid. `The lac thus precipitated is washed well by decantation, filtered and air dried. Bleaching is then carried out as in Example 1. At this stage, the fractionated, bleached soft lac should have an acid value about 81 and a softening-point of about '70 C.

(softening-melting range 7077 C.).

b) Hydrolysis Hydrolysis is carried out as in Example l except at 28 C. for about 50 minutes. The hydrolysed lac which has an acid value of about 160 is then precipitated.. washed, filtered and dried asy in Example 1.

natant liquor and washings are united and acidifled with dilute sulphuric acid. The precipitated lac is well-Washed, filtered, collected and dried. l

Bleaching is carried out as in Example 1. At this stagejthe fractionated bleached soft lac should have an acid value about and a soften ing-point of about 73 C. (softening-melting range 73-80 C.).

(b) Hydrolyss Hydrolysis is carried out exactly as in Example 2, except that the time allowed for hydrolysis The is then precipitated, washed, filtered and dried as in Example 1..

(c) Preparation of backing solution As 1n Example 1.

ExAMPLn 4 (a) Prepare a 35% bleached soft lac resin asv in Example 3.

(b)A Hydrolyse as in Example 3 but continue for 24 hours. This lac has an acid value of about 180 whole lac can be dissolved.`

acid value, hardness, elasticity and viscosity de- A pend largely on the/size and state of polymerization of the molecules. Thus lo-wer polymers have greater solubility and acid value and lower softening-melting range.

The monomeric molecular structure is still not definitely established. It contains .aleuritic and shellolic acids, the former a polyhydroxy acid which can easily esterify with the shellolic acid and in this way very large molecules can be built up. In whole lac it is calculated (from acid value) that the molecular size varies from one of M. W. 300 to M. W. 3,000. The lowest fraction of monomeric acids are viscous liquids, forming the natural plasticizers to the harder portions.v

The highest polymers are insoluble in alcohol. V .It is desirable to obtain a fraction of the lac in which the difference in molecular sizes is not so great as in the whole lac. Complete homogeneity of molecular size is not necessary, but an alkali hydrolysed whole lac is to heterogeneous to be of any value as a backing medium, if Water resistance is required.

Whole lacresin may be separated in various ways into soft lac and hard lac fractions, for` example, by extraction of the lower polymers with toluene or trichlorethylene. The lower polymers with high acid value and low softening point removed leaves a lac of low acid value and high` softening-point. This is known as hard lac resin and the soluble part as soft. lac resin.

A still better method of separation is one based on differences in acidity of the various polymers and consists of extracting with aqueous alkali, eitherhot or cold, the alkalies usedl being sodium carbonate or borax or sodium dihydrogen'phosphate. The amount of lac dissolved is determined by the amount of alkali used-*and up to 100% 4 In practice never more than 30% of the whole lac is removed as otherwise the remaining fraction of hard lac resin becomes insoluble in alcohol: ,The soft and hard lac resins obtained in this way are not greatly different from those obtained by extraction with toluene.

The action of sodium carbonate on the whole lac is not hydrolytic as the amount used is only suflicent to neutralize part of the acid groups already present. Thus it is certain that the fraction of the whole lac called soft lac resin obtained Aby acidification of the alkali extract possesses thel same molecular structure as it did when part of overcoating layer for photographic plates-or film,

it is necessary that the lac, however fractionated. should have a softening point which is not lower than 70 C. Otherwise the layers coated on the plate or film may be tacky. The acid value of the final hydrolyzed lac should be about 130 to 160 although the value for the unhydrolyzed fractionated lac can be anything from to 90, the controlled hydrolysis adjusting it to about 140 to 160 or even 130 to 4180. In order to raise to the desired level, the softening point of a lac of which that value initially was too low, it would be nec,-

essary to polymerise it; alternatively, the partialA oxidation which accompanies bleaching with hy pochlori'te; also serves to raise the softening point". Ordinarily polymerization is attended by a loweringin acid value and is, therefore, undesirable. A' soft lac resin purchased from the firm of A. F. Suterv Company Limited of London, has an acid value of about 90-and a-softening point of about C. and is satisfactory for vthe purposes of our invention.

Hard lac resin usuallyhas a softening point of C. to 85' C. and an acid valueof about 60. Hard lac resin obtained from the firm of A. F. Suter Company Limited of London, has a softening point of C. to 95 C. and an acid value of The acid Avalue can be raised usually by shorter hydrolysis of the hard lac with caustic alkali.

The lac molecule contains, besides free hydroxyl and carboxyl groups. a number of anhydride, lactone and ester linkages. The free acid groups explain the solubility of the lac in dilute alkali on long standing; the acid groups are small compared with the shellac molecule, especially in the case of the higher polymers, so that solution is comparatively slow.` When hot caustic alkali is used, complete hydrolysis takes place not only opening lactone rings but also hydrolyzing anhydride and estery linkages. It was found that hydrolysis with I/2 normal caustic alkali at room temperature for a short period, followed by precipitation with acid, was sufficient toopen out lactone rings and perhaps anhydride linkages, giving a lac with a very high acid value (about 140-160) and a melting point which was slightly higher than that of the original lac. The amount of alkali found to give the most satisfactory result is 80 cc. of 1/2 normal sodium or potassium hydroxide per 10 grams of lac. This amount of alkali is roughly four times the acid value of the lac. i

The eifect of hydrolysis, besides promoting alkali solubility, is also to lower the water re-, sistance. Many natural resins have been investigated and until now fractionated shellac is the only one found which reaches a state-of developer solubility while still remaining between the permissible limit of water permeability.

Colophony on alkali treatment reaches the limit'of water permeability before the stage of complete developer `solubility. Gum dammar and gum lkauri are too heterogeneous and too alkali insoluble to be of useable value. Hard and soft copals, although alkali soluble, hydrolyze very slowly, if at all, and are imperfectly soluble in al- 65 cohol. Fractionation of copals may, however, lead to suitable products.

When, used as antihalation backings or filter layers, the lac resins, according to our invention, may have incorporated various dyes. The following dyes have been tested, with Suters soft l'ac.

Acid Magenta P. (l. C. 1.).-A three hour hydrolysis of the lac is necessary to make the backing overcoating soluble in developer when using this dye. The ratio of dye to lao should 76 not be too high as this renders the backing insoluble.-

Acid Magenta AS (I. C. 1.).-This dye is completely water soluble and bleaches rapidly in the developer. A hydrolysis 'time of 30 minutes for the lac gives an excellent backing .free from bleeding. The amount used is three grams of dye with 10 grams of lac in 25 ccs. of methanol.'

Luzol Brilliant Green BL.-A hydrolysis time of 20 minutes is sufflcient when using this dye.

The ratio of dye to lac should'not exceed 15 to as the backing band becomes insoluble in the developer. The amount used is 1.5 grams dye in l0 grams of hydrolyzed lac and 25 cc. methanol.

Methyl Blue (Ink blue) .--This dye is water soluble and can be incorporated in a lac resin which has been hydrolyzed for one hour. The amount used is` 1.5 grams of dye in 10 grams of hydrolyzed lac and 20 cc. of methanol.

Our invention will now be described with particular reference to the accompanying drawing.

As shown in Fig. 1 thereof, 10 is a suport of glass or celulosic medium having -on one side thereof an emulsion layer II and on the opposite side an antihalation backing layer of hydrolyzed lac resin containing a suitable dye;

Fig. 2 is a, multi-layer film in which emulsion layers I3 and I4, sensitized to record different regions of a spectrum are coated on the support I0. A. filter layer I5 of hydrolyzed lac resin containing a suitable filter dye is coated over the emulsion layerv le;

Fig. 3 represents a modification of our invention in which the lac resin is used without coloring material as an overcoating or protective layer which is removed in the developer. As shown therein, the `support I0 carries the emulsion layer I I and the overcoating layer i6 of hydrolyzed lac resin not containing a coloring material.

t0 be taken as limited 1. A photographic .element comprising a support having thereon a sensitive emulsion layer and a layer coated directly over said emulsion Suitable dyes are readily decolorl layer comprising a partially hydrolyzed lac resin having a softening point of not less than '10 C. and an acid number of approximately to 180.

2. A photographic element comprising a sup.- port having thereon a sensitive emulsion layer and a layer of al partially hydrolyzed lac resin having a softening point of not less than 70 C.

and an acid number of approximately 130.120 180,

said lac resin -layer containing a filter dye uniformly dispersed therein. v

3. A photographic element comprising a transparent support having on one lside thereof a sensitive emulsion layer and on the other side thereof an antihalation layer of a partially hydrolyzed lac resin containing a filter dye uniformly dispersed therein. said lac resin having a softening point of not less than 70 C. and an acid number of approximately to 160.

4. A photographic element comprising a cellulose ester film base having on one sidethereof a sensitive emulsion layer and on the other side thereof an antihalation layer of a jpartially hy-fdrolyzed lac resin containing an antihalation dye uniformly 'dispersed therein, said lac resin having a. softening point of not less than 70 C. and an acid number of approximately 130 to 160.

5. A photographic element Vcomprising a'cellu'- lose Vester film base having on one side thereof a sensitive emulsion layer and on the other 'side thereof an antihalation layer of a partially hydrolyzedsoft lac resin containing an antihalation dye uniformly dispersed therein, said soft lac resin having a softening point of not less than 70 C. and an acid number of approximately 130 to 160. r

6. A photographic element comprising a celluf lose ester lm base having on one side thereof a sensitive emulsion layer and on the other side thereof an antihalation layer of a partially hydrolyzed soft lac resin containing an ant-ihalation dye uniformly dispersed therein, saidv soft.

DEREK E. n. AYREs. ALAN BAILEY. l EDWARD B. KNQ'I'I. 

